The invention relates to a method for protecting vehicles (particularly leased or hire vehicles), against unauthorized use, by broadcasting a use enabling signal from a stationary master information station.
Such a protection arrangement is disclosed for example in German patent document DE-A 44 40 975.3-51, in which an anti-theft control unit and a receiving device of a mobile communication system are arranged in the vehicle. A communication structure aboard the vehicle permits, on the one hand, the exchange of data between an anti-theft control unit and the receiving device and, on the other hand, the exchange of data between the anti-theft control unit and at least one operationally necessary control unit of the vehicle. As long as a vehicle has not been reported stolen, or provided another unauthorized use of the vehicle has not been determined, signals are transmitted from a master station to the vehicle via the mobile communication system at regular time intervals, the said signals being received by the receiving device. The reception of the signals is conveyed from the receiving device to the anti-theft control unit via the communication structure. The signals are detected and if they are determined to be directed at the vehicle, operation of the vehicle is enabled for a prescribed time period interval between two which is longer than the time successive signals. If no signal is received before expiration of the period for which operation of the vehicle is enabled, the enabling of operation of the vehicle is not prolonged. The anti-theft control unit then actuates the at least one operationally necessary control unit via the communication structure and prevents the further operation of this control unit, at least at the next attempt to activate the vehicle.
This measure prevents a vehicle from being used without authorization over a relatively long period of time. Also, operation is not dependent on signals which are emitted by the vehicle and may be disrupted, but is instead dependent exclusively on reception of the signals broadcast by the master station so that disruption or destruction of the communication system does not permit prolonged use of the vehicle.
A disadvantage of this method is that it does not enable a location of the vehicle. As a result, it is still possible, for example after misappropriating the vehicle, to transfer it to another location on a transporter, without risk. In addition, a relatively long period of time may pass between the time when the unauthorized use of the vehicle starts and the time when the information relating to the unauthorized use is conveyed to the master station, so that broadcasting of the signals may not commence until a considerable period of time after the unauthorized use has started. During this period of time, the unauthorized use of the vehicle can be continued unhindered. In addition, if a large number of vehicles are to be protected in this manner, a very large transmission capacity is required for the signals which are broadcast at regular time intervals. Therefore, this method is suitable only for protecting a strictly limited number of vehicles.
Furthermore, it is known for example from the article xe2x80x9cSatellitenhilfe gegen Auto-Klauxe2x80x9d [Using satellites to combat car theft] by R. Gramm in the journal Funkschau Issue 16/1993 pp. 42 to 45 to provide a locating system which is arranged on the vehicle and determines, continuously or at regular intervals, the geographic area where the vehicle is located, and conveys this information to a master station via a transmitting device aboard the vehicle end. A receiving unit for receiving and evaluating the locating information broadcast by the transmitting device is present in this master station. The location of the vehicle can thus be monitored continuously or at regular intervals in the master station.
This device has the disadvantage that it provides no arrangement for disabling the vehicle. The tracking of the vehicle by the master station can also be prevented, for example, by destroying the transmitting device at the vehicle end or the locating system. In addition, a large capacity in terms of transmitting devices and transmitting frequencies must be made available if a large number of vehicles are to be tracked continuously. If for example a digital radio telephone is used as the mobile communication system, high communication costs are incurred in order continuously to convey the results of the locating of the vehicle to the master station.
German patent document DE 42 24 536 A1 discloses a system for the geographically defined limitation of the area of movement of vehicles. Here, signals are received from satellites by means of a receiver, which signals are converted into position coordinates in the vehicle and compared with defined prescribed values. If a vehicle leaves a previously defined geographic area, a Motronic system which controls the drive system is blocked by means of an evaluation unit and at the same time the current location of the vehicle is transmitted to a control center by means of a transmission unit.
A disadvantage of this arrangement is that the limitation of the area of movement has to be defined in advance, and cannot readily be changed during the period of use. In addition, it is disadvantageous that measures are only taken for the possibility of the vehicle leaving a specific geographical area which may not be adequate for specific applications. Furthermore, no measures are provided to address the possibility that the receiver may be tampered with or destroyed.
German patent document DE 43 20 174 A1, describes a method for protecting operation of a motor vehicle by the authorized user, in which a vehicle transmits a test signal to a master station which replies with a confirmation signal. If the confirmation signal is not received by the vehicle, then, except in specific exceptional cases, an operation disabling device is triggered making operation of the vehicle impossible.
The risk of unauthorized use is particularly great in the case of hire vehicles or leased vehicles as well as in the case of other vehicles which are not used by the owner himself, and also in the case of taxis or lorries.
An object of the invention is to prevent reliably the unauthorized use of a vehicle, in particular of a hire vehicle or leased vehicle.
This object is achieved by the method in accordance with the invention, in which a master station broadcasts a signal defining use restrictions applicable to the vehicle in question. A use protection control unit aboard the vehicle checks for violation of the use restrictions, and disables at least one operationally essential vehicle control system if a violation is detected.
According to another feature of the invention, use of the vehicle is possible only it before the vehicle is handed over (before a journey is begun in the case of taxis and lorries), a bidirectional communication takes place between the vehicle and master station, and takes place at a later time as well. As a result, it is possible not only to transmit exclusively a position message of the vehicle to the master station or to transmit exclusively enabling signals to the vehicle from the master station, but it is also possible to make the communication appropriate to requirements. Before the vehicle is handed over, the use restriction or restrictions applicable to the vehicle must be defined. Operation of the vehicle is not possible until this use restriction is defined.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.